1. Field of the Invention
The present invention relates to a control apparatus for controlling the density of toner in a developing unit used in copy machines, laser printers or like image forming apparatus that forms images by toner development.
2. Description of the Prior Art
Conventionally, toner concentration detecting sensors for detecting developer toner concentration have been provided in the toner transport section within the developing unit and toner accommodating section to enable development with uniform image density. Toner is supplied to the developing unit in accordance with the toner concentration detected by said toner concentration detecting sensors. Thus, the developing material toner concentration can be stably maintained within the developing unit.
However, accurate detection of toner concentration cannot be achieved due to toner accumulation and adhesion to the top of the sensor. For these reasons an elastic cleaning blade or brush is attached to the support shaft used for transport/mixing of the developing material so as to clean the surface of the sensor by making rubbing contact with the surface of said sensor in conjunction with the rotation of the support shaft.
However, the cleaning member becomes bent and folded because it makes repeated rubbing contact with the toner concentration detecting sensor, making proper operation impossible. Further, toner concentration detecting sensor output may not be input to the microcomputer or other control device due to disconnection or a breakdown of said sensor itself. Consequently, if for some reason the cleaning member does not operate, the output from the toner concentration detecting sensor increases, toner concentration is judged to be low, and toner replenishment is excessive. The developed toner image therefore attains an extremely high concentration and the toner overflows the developing unit and soils the surrounding region.
Further, a breakdown which impedes sensor output being input to the microcomputer controller leads to a determination that toner concentration is high, and results in extremely low toner image density after development because toner replenishment has been discontinued.